Devices of this type are, in addition to other uses, used for pressure measurement in aggressive media. The dividing membrane is contacted with an aggressive first medium and the pressure prevailing in the first medium is transferred to a second medium in the pressure chamber. There, the pressure is conducted over a suitable pressure conducting line to a pressure measurement cell. Pressure transfer using a pressure transmitter and an attached pressure line can, however, also be desired in the case of non-aggressive media, for bridging large distances between the first medium and the location of the pressure measurement cell.
Incompressible oils are preferably used as the second medium for pressure transmission. In so far as such a substance is suited for contaminating a medium being measured, and for various other reasons, it is necessary to recognize early that there is a leak in the dividing membrane, or a rupture of the dividing membrane. To this end, Bastiaan discloses in the European patent application EP 0 838 672 a pressure transmitter, in which the pressure chamber has in its wall a dead-end hole, in which the electrode of a conductivity sensor is arranged. In such case, when the dividing membrane breaks, the first medium diffuses into the pressure chamber and into the dead-end hole, whereupon a change in the conductivity is detectable, provided that the first medium has a conductivity which deviates significantly from that of the second medium. This is especially the case, when the first medium is a corrosive medium and the second medium is an oil.
For the various pressure measurement applications, there is an immense number of pressure transmitters, which are fitted to the different demands of the applications. A very high manufacturing cost is required to equip this multiplicity of sensors with the conductivity probe proposed by Bastiaan. Additionally, the arrangement of Bastiaan needs a minimum diameter of 1.5 inches, or 3.8 cm, for placing the conductivity sensor next to the pressure conducting line, as follows from the applicant's product description “Badoterm's MDS Diaphragm Leakage Detection System” for a product corresponding to the subject matter of the application. Such a constraint is unacceptable for many applications.
Moreover, transport of the contaminants to the sensor happens purely diffusively in the described pressure transmitter. This can lead to a large time delay between the occurrence of a leak and the detection of the contamination resulting therefrom, depending on the depth of the dead-end hole and the particulars of the installation of the pressure transmitter.